1. Field of the Invention
The present invention relates to a flexible pipe joint for subsea risers and pipelines, and in particular, such a flexible pipe joint that is capable of long-term operation when subjected to temperatures greater than about 180° F. (82° C.).
2. Description of the Related Art
Offshore production facilities typically use risers constructed of rigid pipe sections and flexible joints for conveying production fluid such as oil or gas from a well on the seabed to a floating offshore production platform. This construction, for example, permits a pipeline to be laid under water and then raised for connection to the offshore production platform.
Typically, a flexible pipe joint has a laminated elastomeric flex element including alternating layers of elastomer and steel plates. The elastomer is bonded to the steel plates and the steel plates are encapsulated in the elastomer. The elastomer is typically vulcanized natural rubber, synthetic rubber, or mixtures of natural and synthetic rubber. Such flexible pipe joints have been designed and manufactured for a service life of at least twenty years under low temperature conditions.
As described in Whightsil, Sr. et al., U.S. Pat. No. 5,133,578, the flexible pipe joint may also include a bellows to isolate the elastomeric flex element from gases in the production fluid. For example, if the elastomer were exposed to high-pressure production fluid containing low molecular weight gasses such as methane, explosive decompression could occur upon sudden release of the high pressure, causing gas molecules captured in the elastomer to expand and cause local ruptures in the elastomer surface.
Recently there has been a need for flexible pipe joints that are capable of long-term operation when subjected to temperatures greater than 180° F. (82° C.). In particular, wells are being drilled into the seabed at depths of more than 1000 meters in the Gulf of Mexico and off the shore of Nigeria. It is desired to use flexible pipe joints in risers for delivering production fluid from the wellhead on the seabed to a floating platform. However, the planned depths of the wells below the seabed and the desired high flow rates would cause the temperature of the production fluid to substantially exceed 180° F. (82° C.). In addition, the ambient seawater temperature is relatively high (80 to 85° F. (27 to 29° C.)). If a conventional flexible pipe joint were used to convey the production fluid, the flex element in the flexible joint would be continually subjected to temperatures in excess of the usual limit of 180° F. (82° C.). This would cause the service life of the conventional flexible pipe joint to be severely degraded. Therefore, there is a desire for a high temperature flexible pipe joint that would have a service life of at least twenty years when conveying production fluid at temperatures considerably in excess of 180° F. (82° C.).